[mono] Add iOS app sample using mono runtime

[mdh1418]

Summary

This PR looks to port over the iOS sample from dotnet/runtime to highlight the concept of building applications on top of the mono runtime.
A recent version of XCode as well as an iOS device or simulator is required to run the sample with dotnet publish.

The sample will depend on a NuGet Package containing the files that build the app and embed the mono runtime into the app, and the code that will build that package can be found here dotnet/runtime#43048

[adegeo]

Thanks for adding this example. There are some changes you'll need to make so that this sample shows in the samples browser.

[adegeo]

Also need the URL it will be hosted at in the samples browser when published: https://review.docs.microsoft.com/en-us/samples/browse/?branch=master

Suggested change

	description: "An iOS application that contains an example of embedding the mono runtime to invoke unmanaged code with C#."
	description: "An iOS application that contains an example of embedding the mono runtime to invoke unmanaged code with C#."
	urlFragment: "mono-ios-csharp"

[mdh1418]

Will the url be generated automatically from adding this line or are there other actionables I need to take to get the sample hosted at the url?

[adegeo]

IFAIK you just need to add this line. I have heard rumors though that the samples browser doesn't automatically import samples and you need to file a ticket. I've heard it's "supposed" to be automated but it never shows up and when you ask about it, it magically shows up, as if someone is somewhere pushing a button every time.

@IEvangelist true?

[IEvangelist]

My experience is that it takes a long time, roughly a week or so - but it does eventually make its way there. There have been a few times too where it has gotten stuck with no reason why, then you have to ask the right people who have access to get it moved.

[adegeo]

Right now this needs to be dotnet-core so that it appears in the filter list for the samples browser. There isn't a product filter for ios and mono runtime unfortunately. We'll need to do something about this in the future though: https://review.docs.microsoft.com/en-us/samples/browse/?branch=master&expanded=dotnet&products=dotnet-core

Suggested change

	products:
	- dotnet
	- iOS
	- mono runtime
	products:
	- dotnet-core

[mdh1418]

Will there be dotnet5 or dotnet6 added to the product filters in the future?

[adegeo]

No idea. I don't have anything to do with the samples. I'll bring this up to our team and see what they know.

[adegeo]

#3939 needs to be merged to fix the build error.

[adegeo]

I think this is looking good now. Some minor things to adjust.

[akoeplinger]

Left a few comments, looks good overall :)

[akoeplinger]

Looks like this doesn't work on CI because this repo installs the 5.0 dotnet sdk. I tried locally and what works is using $(BundledNETCorePlatformsPackageVersion) as the version since then it'll try to get the same version as it uses for the runtime pack.

That brings up another issue though, right now it tries to restore Microsoft.NETCore.App.Runtime.ios-x64 with version (= 5.0.0) but the final 5.0 release isn't published to nuget.org yet. And even if it were we don't really want to use the 5.0 version.

As far as I know the only way to consume 6.0 assets is by installing nightly master builds of the dotnet sdk from the dotnet/installer repo. I don't know if we want to do that in CI in this repo (maybe we just need to skip this project there).

Additionally we can add the following global.json next to Program.csproj to force usage of the 6.0 SDK:

{
  "sdk": {
    "version": "6.0.100-alpha",
    "rollForward": "major",
    "allowPrerelease": true
  }
}

[steveisok]

@adegeo Tagging you because you made the last commit to the CI yml. Can we add another leg that installs the net6 preview sdk and builds the iOS project? That seems to be the only way to be correct on CI for us. Otherwise, we can just skip the project.

[adegeo]

@steveisok Sorry, missed this alert. Yeah we could do that easily as long as the dotnet-install powershell script supports it?

[steveisok]

@adegeo Looks like it does with the --version switch. Would it be easier to bump the sdk version in CI or just add another leg?

[adegeo]

@steveisok If you can give me the exactly command line I'll edit the script to add a leg. I tried .\dotnet-install.ps1 -version 6.0.100-alpha but it didn't work

[mdh1418]

Fixed the version at 6.0.100-alpha.1.20531.2.

[adegeo]

Depends on #3941

[adegeo]

Once we address the comment I made about installing .NET 6, I think we can merge this.

[adegeo]

@steveisok @mdh1418 @akoeplinger
Considering it's not easy to install the .NET 6 SDK at the moment, I would improve this with the specific commands to install. I don't see anyone figuring out how to install. I couldn't and had to have @steveisok help.

[mdh1418]

Added more details to install the specific dotnet version. Was this what you meant?

[mdh1418]

@adegeo I made a few more changes and think this PR is ready for another look over.